The so-called “dieselgate” revelations in 2015, which disclosed that Volkswagen and other manufacturers used “defeat devices” to hide that their diesel cars were emitting too much nitrogen oxide (NOx), heightened public awareness of the problem of NOx emissions from diesel cars, trucks, and buses.

But this is not only a defeat device problem. Both light-duty and heavy-duty diesel vehicles emit more NOx in on-road driving conditions than during laboratory certification testing, for reasons that may range from details of the engine calibration to equipment failure, inadequate maintenance, tampering by vehicle owners, the deliberate use of defeat devices, or simply deficient certification test procedures.

Lack of data – until now

There has been a lack of solid quantitative data about the effects of diesel vehicle excess NOx emissions, both in terms of public health and environmental impacts – until now. A study published today in Nature, co authored by SEI experts, examined 11 major vehicle markets representing more than 80% of new diesel vehicle sales in 2015 (Australia, Brazil, Canada, China, the EU, India, Japan, Mexico, Russia, South Korea, and the U.S.) and found that those vehicles emitted 13.2 million tons of NOx under real-world driving conditions—that’s 4.6 million tons more than the 8.6 million tons expected given the vehicles’ performance under official laboratory tests.

“Heavy-duty vehicles—commercial trucks and buses—were by far the largest contributor worldwide, accounting for 76% of the total excess NOx emissions. And just five markets (Brazil, China, the EU, India, and the U.S.) produced 90% of that. For light-duty vehicles—passenger cars, trucks, and vans—the European Union produced nearly 70% of the excess diesel NOx emissions,” said Josh Miller, researcher at the International Council on Clean Transportation (ICCT) and co-lead author of the study.

NOx is a key contributor to outdoor air pollution in the forms of ground-level ozone and secondary fine particulate matter (PM2.5). Long-term exposure to these pollutants is linked to a range of adverse health outcomes, including disability and years of life lost due to stroke, ischemic heart disease, chronic obstructive pulmonary disease, and lung cancer—particularly in sensitive populations such as the elderly, who are at higher risk of chronic disease.

"This highlights the importance of vehicle emission standards and the stark consequences of these standards not being met."

Dr Lisa Emberson Co-author Lisa Emberson, Senior Research Associate at SEI York, said “This highlights the importance of vehicle emission standards and the stark consequences of these standards not being met. The study found that between 31% and 50% of NOx produced by diesel vehicles were above official certification limits, and were associated with 38 000 premature deaths worldwide in 2015.

The EU was found to have a particular problem with light duty vehicles which accounted for around 70% of total excess NOx from LDVs, causing the EU, along with China and India, to suffer disproportionately large shares of the global health impact.”

Co-author and SEI Researcher Chris Malley said, “This study also shows that these excess diesel NOx emissions also effect crop yields, in addition to human health impacts, and estimates that implementing Next Generation standards could reduce losses in crop production by 1–2% for Chinese wheat, Chinese maize, and Brazilian soy, and result in an additional 4 million tonnes of crop production globally.”

Government action could save nearly 200,000 lives

At a global level, the study projects that the impact of all real-world diesel NOx emissions will grow to 183,600 early deaths in 2040, unless governments act. In some countries, implementing the most stringent standards—already in place elsewhere—could substantially improve the situation, according to the researchers.

“Globally, the single most important action to reduce the health impacts of excess diesel NOx emissions is for countries to implement and properly enforce a Euro VI tailpipe emission standard for heavy-duty vehicles. Combined with strengthened compliance for light-duty vehicles and next-generation standards, this would nearly eliminate real-world NOx emissions from diesel vehicles, which would avoid 174,000 air pollution-related deaths and 3 million years of life lost worldwide in the year 2040,” said Ray Minjares, co-author and Clean Air Program Lead at ICCT.

Notes to editors:

The study was led by the International Council on Clean Transportation and Environmental Health Analytics, LLC., in collaboration with Stockholm Environment Institute, the University of Colorado, and the International Institute for Applied Systems Analysis. Funding for the study was provided by the Hewlett Foundation, ClimateWorks Foundation, European Climate Foundation, Energy Foundation China, and the NASA Health and Air Quality Applied System Team.